1. Field of the Invention
The invention relates to methods of and apparatus for the comminution or disintegration of solid materials and more particularly to impeller bar installations in impact crushers.
2. Discussion of the Prior Art
Comminution apparatus referred to as "impeller type impact crushers" use impeller rotors having impeller bars which are typically disposed circumferentially and evenly spaced about an axis of a respective rotor to revolve thereabout. During operation of the crushers, the bars are caused to impact with material to be comminuted. A particular use for impeller type impact crushers is, for example, as comminution apparatus for rocks in the production of aggregates for construction materials such as concrete or asphalt materials.
Abrasive characteristics of the materials to be comminuted typically cause substantial wear on impeller bars and on other related machine elements which are exposed to contact by the materials. Also, the impact of hard rock materials with the impeller bars may cause the bars to crack. Ease of replacement and ease of adjustment for wear of impeller bars and their related elements are consequently of constant concern to those engaged in seeking to advance the art of comminuting solid materials.
Securing impeller bars to either "solid" cast type or "open" type rotors appears to be contemplated in most instances with wedges. In implementing arrangements, the interaction of elements of various available structural arrangements varies widely. Various known rotor securing arrangements, while addressing a particular problem of one type or another, fail to address other problems. Other arrangements may suffer from complexity, excessive weight poor accessibility for inspection, adjustment or replacement, the latter being further adversely affected by a condition of "liming," which relates to the build-up of stone fines which adhere to the crusher elements as a tough crust, increasing the difficulty of adjustment or replacement.
Certain problems arise because impact crushers may be used to comminute one type of rock and then be switched to comminute another type of rock, for example upon a shift to another job site at which the available rock material has different characteristics. A contractor may prefer a tough yet not quite as abrasion resistant impeller bar material for use on a certain type of rock to avoid cracking the impeller bars, while a hard material may yield better results for another type of rock. Often, materials offering the least wear or maintenance can be determined only after the comminution work of rock material at a new job has begun and the maintenance intervals are compared with logged historical maintenance data.
A problem which afflicts crushers is that they are specific in their application to handle a certain material and that cumbersome changes may need to be made to a crusher to adapt the crusher to replacement parts which may differ slightly in size from those for which the crusher was originally designed.